1. Field of the Invention
The present invention relates to an electrolytic cell useful for the production of a halogen and an alkali metal hydroxide from an alkali metal halide aqueous solution or oxygen and hydrogen from an aqueous alkaline solution, and particularly to a filter press type membrane electrolytic cell.
2. Description of the Prior Art
Various filter press type membrane electrolytic cells are known in which a number of anodes and cathodes are alternately arranged in parallel to one another and partitioned from one another by a cation exchange membrane.
On the other hand, a so-called electrodialysis operation has long been known in which an aqueous solution containing ions are supplied to two compartments partitioned by an ion exchange membrane, and an electric field is applied to remove the ions or to concentrate useful ions. It is practically employed for the production of sodium chloride from sea water or as a technique to obtain fresh water from sea water. Electrolysis is substantially different from the case of an electrodialysis cell in that it involves an electrode reaction on the surface of an electrode and the presence of an electrode surface is thereby essential, and in the electrolysis of an alkali metal chloride aqueous solution, a chlorine gas is generated at the anode and a hydrogen gas is generated at the cathode.
In a conventional filter press type electrolytic cell, it is known to use e.g. angular hollow pipes constituting passages for an electrolytic solution and electrolized products and joined to form hollow rectangular frames defining electrode compartments, i.e. so-called hollow compartment frames.
The electrolytic cell having such hollow compartment frames is fairly effective and useful. However, the compartment frames are manufactured from hollow pipes of expensive material, and accordingly, the cost of the cell becomes inevitably high involving the expensive material and manufacturing costs.
A so-called plate type electrolytic cell has been proposed to overcome the disadvantage of the abovementioned pipe type electrolytic cell, in which a rectangular frame gasket made of a plate is used as the compartment frame. An electrolytic cell of this type is disclosed in e.g. Japanese Laid-Open Patent Application No. 108899/78, in which compartment frame gaskets made of a non-conductive flexible plate material and having a center opening constituting an electrolytic compartment, are assembled with cation exchange membranes and electrode plates to form a filter press type electrolytic cell, and the respective compartment frames, electrode plates and cation exchange membranes are provided, at their four corner portions, with holes constituting passages for the electrolytic solutions and the electrolyzed products.
From the aspect of the manufacturing costs, the electrolytic cell of this type is substantially advantageous over the abovementioned cell in which hollow pipes are used. However, it has certain drawbacks in the structures of the electrode plates and the compartment frames.
Namely, in the electrolytic cell of the type disclosed in the abovementioned Japanese Laid-Open Patent Application, the electrode plates have the same size as the compartment frames, and accordingly it is necessary to provide holes not only on the compartment frames but also at the four corners of each electrode plate to constitute passages for the electrolytic solution and the electrolyzed products. This brings about not only an economical disadvantage that a great amount of expensive electrode plates is required but also a fatal defect. Namely, with respect to the anode plates in order to prevent electrical short circuit, it is necessary to electrically insulate the passages formed on the anode plates for the cathode solution and the cathode products from the anodes. Likewise, with respect to the cathode plates, it is necessary to electrically insulate the passages formed on the cathode plates for the anode solution and the anode products from the cathodes. In this respect, the abovementioned Japanese Laid-Open Patent Application states that it is necessary to form the passages with a resin, e.g. a fluorine-containing resin such as Teflon to establish the required electrical insulation. However, it is quite cumbersome to form such portions of the electrode plates with a material of different nature, and such an operation is economically extremely disadvantageous.